I will tell you it isn’t an easy road for Li-Po, what I mean is it isn’t cheap. Though I will admit some internals that I have worked with have impressed me. The number one thing everyone says is the gears will shed, not necessarily, if they are of high quality (or a good batch of cheap internals) and "SHIMMED" properly you shouldn't have any problems with a Li-Po shredding gears. The other problem that they may cause is wear on the piston if it doesn’t have metal teeth, if you think about it when the gears are moving faster at a higher torque you may catch the plastic piston on a tooth and deform it causing it to break.

The only problem that is tricky to avoid is the fact that Li-Po has a very high current compared to normal batteries, so your contacts will have to be changed out periodically because they will burn out faster than with normal batteries.
There is only one cure to this problem that allot of airsofters are kind of edgy about getting into, it’s a mosfet. A mosfet is an electronic device that is used as a timed relay taking a small amount of current to the trigger contacts(Causing allot less wear) and supplying the rest(sometimes restricted if current is to great) to the motor for a faster, cleaner, and more efficient cycle of an AEG. If you look on YouTube you will see what I am talking about.

EDIT: A mosfet can allso be used to turn a single/full settings into single/3rnd, 3rnd/full, single/single, single/full, single delay, single/single(delay)full
many combinations can be acheived depending on which one you get

M140
If you are at this point you are either getting a Pro to do it or very knowledgeable at this point.

This is only my info on Li-Po, someone may have more. I would suggest that if you are a beginner please stay away from Li-Po. They are very tempting, but you will spend more money than you want to if you do not have your gun setup in the right places. Li-Po is a safe battery if you respect it, but if you don’t watch it or treats it right there will be lots of ways you can mess up your gun. I run a Li-Po and always will now with my guns, just most of my guns I have are limited on battery space and I need more shots per battery which is why I turned to them in the first place.

they dont have the 7.4v in yet but I am waiting on it for my CQB guns.

And in my opinion Tynergy is the way to go for Li-Po or NiMH batteries. I have used Intelect and they are good but they dont seem to last long or hold a charge very well, plus they dont make Li-Po that i know of yet.
Edit: Intelect does make a Li-Po, but they package it diferently. Comes in a yellow plastic shell with a red label.

All the major lipo brands are from china.......100 bucks is the markup for shipping and to turn a profit.

http://spcracing.com/
idk this is my local dealer he makes all our custom packs for raceing rc cars and they will work in the guns and i woll almost garentie that if you ask he will make them to fit you gun if you order enough. also there only like $50 for a 7.4 5000mAh packs

and as for the NiMH packs it all depends on how ther wired and how well you take care of them as for there life. usualy with in 30days of a full charge a NiMH pack will have discharged its sel to almost nothing. but there are ways of bringing it back to life. this is usualy done by chargung and dis charging the pack several times. but if your not carfule and dont use the right eguipement you can fry the pack. the most commen way of doing this is over peaking a pack.

ill use one of my high proformance race packs and charges as an example of over peaking. lets say you have a 7.2v 4200mAh battery pack in your gun that you need for an upcomming game. so you charge it at 5.0A on a smart charger and 30min later it peaks only adding 3500mAh to the pack BUT your not there when it peaks to take it off so when you show up to remove the pcak you peak it again because you know that all the time from the stop of the charge to know the battery has lost some power. so you repeak it and this time anouther 900mAh is added to the battery.now this is fine as long as you dont do it continously or more than once per charge. when you continously over peak a battery you end up dammanging the cells and thus the life is shortened and the pack dies faster.

as for my personal prefrences on cells for big packs useing large cells i use enere 4600mAh matched cells made into custom packs by myself. but for lipo i use only spc packs

http://spcracing.com/
idk this is my local dealer he makes all our custom packs for raceing rc cars and they will work in the guns and i woll almost garentie that if you ask he will make them to fit you gun if you order enough. also there only like $50 for a 7.4 5000mAh packs

and as for the NiMH packs it all depends on how ther wired and how well you take care of them as for there life. usualy with in 30days of a full charge a NiMH pack will have discharged its sel to almost nothing. but there are ways of bringing it back to life. this is usualy done by chargung and dis charging the pack several times. but if your not carfule and dont use the right eguipement you can fry the pack. the most commen way of doing this is over peaking a pack.

ill use one of my high proformance race packs and charges as an example of over peaking. lets say you have a 7.2v 4200mAh battery pack in your gun that you need for an upcomming game. so you charge it at 5.0A on a smart charger and 30min later it peaks only adding 3500mAh to the pack BUT your not there when it peaks to take it off so when you show up to remove the pcak you peak it again because you know that all the time from the stop of the charge to know the battery has lost some power. so you repeak it and this time anouther 900mAh is added to the battery.now this is fine as long as you dont do it continously or more than once per charge. when you continously over peak a battery you end up dammanging the cells and thus the life is shortened and the pack dies faster.

as for my personal prefrences on cells for big packs useing large cells i use enere 4600mAh matched cells made into custom packs by myself. but for lipo i use only spc packs

When u say make u mean he has them made. A local race shop does not have the equipment to make a polymer battery. Those packs look like the custom store packs droll all battery.com or a simalar site that makes custom labels for a store when orderd in bulk. And your spelling is horrendous!!!!

When u say make u mean he has them made. A local race shop does not have the equipment to make a polymer battery. Those packs look like the custom store packs droll all battery.com or a simalar site that makes custom labels for a store when orderd in bulk. And your spelling is horrendous!!!!

this isnt a local hobbie shop this is a real company that he runs. our Lhs is a dealer for him but he runs the buissnes.and if you looked at the link it tells you how to care for all diffrent types of batteries that we use in airsoft. and i know my spelling is bad i blame my crappy hs education on that.

This battery pack is safe if you follow these instructions. However if you do not respect the warnings and follow the instructions closely, as with all batteries there is a risk of explosion, fire, smoke emission and poisoning. DO NOT leave a charging battery pack unattended.

Use only chargers for LiPo batteries that utilize a CC/CV method with a cut-off function. The charge cycle will begin with continuous current (CC). When a certain cut-off voltage is reached, the charger will hold the voltage constant (CV) while decreasing the charge current until the pack is fully charged. Your charger must be set to LiPo mode and you use specify the correct number of cells in the pack. A 2S pack has 2 cells, 3S has 3 cells, etc. We recommend any charge rate up to 2C; this means the maximum charge current is 10-Amps for our 5000 mAh capacity LiPo battery pack and 16-Amps for our 8000 mAh capacity LiPo battery pack. Do not use higher charge rates! Charge in LiPo Sack or similar safety device at all times. Cell balancing is a way of ensuring your Li-Po will deliver the maximum performance and capacity over time. Balancing is absolutely necessary and required each and every time you charge the battery pack! The balancing connectors (white) are: JST XH3 for 7.4V packs and JST XH4 for 11.1V packs. If using a stand-alone type balancer, balance the pack BEFORE and DURING charging.

This LiPo battery pack must under no circumstances be discharged after use; doing so will permanently damage the pack. Do not disassemble packs. Do not continue to use a pack if an abnormality is detected, such as foul odors, pack deformation, discoloration and so on. If a pack gets wet it can potentially malfunction, do not use a wet pack. Do not solder directly to cell tabs.

When not used, this LiPo battery pack should be charged to approximately half maximum capacity, then placed in a LiPo Sack and stored in a cool dry area. Check LiPo battery pack every 2 months during long term storage.

A LiPo battery pack is VERY sensitive to being over-discharged. The recommended minimum cut-off is 3.0 Volts per cell, however for a 2 cell pack SPC recommends a Low Voltage Cutoff (LVC) setting of approximately 6.4 volts; or for a 3 cell pack set to approximately 9.6 volts. NEVER run the pack down until your RC car is just barely moving. Stop driving when you notice the vehicle slowing and/or the motor begins losing power. Remove the battery from the car and allow it to cool to room temperature before re-charging. NEVER let the battery rest for a few minutes and then continue driving without first re-charging. Li-Po packs are designed for operating temperatures not to exceed 40°C.

Lithium Polymer batteries do not have a hard steel case like a NiMH battery. Instead a special aluminum foil encloses them, therefore they do not vent. If the integrity of the battery is compromised swelling will occur. If the battery pack is damaged and the case begins to expand, discontinue use immediately and dispose of battery pack properly. Do not touch any liquid if there is leakage.

I stopped into the local R/C hobby store. They looked at me funny when I said Airsoft LiPo batteries packs are 50-100 bucks.

Very helpful thread thus far. I'm excited to see original content.

same, i went to the store about 5 miles from my house to look for a charger, when i told the guy i was getting my lipo and Nimh packs for less than his cost he called me a liar, a quick look at my e-mail recipts and he was speachless...just because someone owns a shop does not mean they know jack **** about anything...to this day the shop owner still will not accept the fact my batteries are 75% less than his were and when i let a few guys borrow them to race with they outperformed all the shops batteries.